The use of delivery devices or introducers employing catheters has long been known for a variety of medical procedures, including procedures for establishing, re-establishing or maintaining passages, cavities or lumens in vessels, organs or ducts in human and veterinary patients, occlusion of such vessels, delivering medical treatments, and other interventions. For these procedures, it has also long been known to deliver an implantable medical device by means of a catheter, often intraluminally. For example, a stent, stent-graft, vena cava filter or occlusion device may be delivered intraluminally from the femoral artery for deployment. For procedures in which a prosthesis or other medical device is implanted into a patient, the prosthesis to be implanted is normally held on a carrier catheter or cannula of the introducer in a compressed state and then released from the carrier catheter so as to expand to its normal operating state, prior to withdrawal of the catheter from the patient to leave the prosthesis in position. In many devices, the steps to carry out the implantation my occur, for example, first by retracting a retractable sheath to expand or partially expand the prosthesis, and then performing further steps to, for example, release one or both ends of the prosthesis, deploy an anchoring stent, or the like. In most cases, it is desirable that such deployment steps follow a specific order as instructed by the manufacturer of the device, but the user of the device is often not restricted from performing steps out of order, and often may do so. Thus, it is desirable to provide a delivery device having a handle assembly that permits controlled and sequential release and deployment of a prosthesis from the delivery device.